1. Field of the Invention
The present invention relates to a system and method for identifying potential hidden node problems in a multi-hop wireless ad-hoc communication network, such as an 802.11 network. More particularly, the present invention relates to a system and method for identifying nodes of a wireless ad-hoc communication network whose capabilities of receiving data packets can be adversely affected by hidden node problems, in order to avoid selecting paths containing those potentially problem nodes for routing data packets.
2. Description of the Related Art
In recent years, a type of mobile communications network known as an “ad-hoc” network has been developed. In this type of network, each user terminal (hereinafter “mobile node”) is capable of operating as a base station or router for the other mobile nodes, thus eliminating the need for a fixed infrastructure of base stations. Accordingly, data packets being sent from a source mobile node to a destination mobile node are typically routed through a number of intermediate mobile nodes before reaching the destination mobile node.
More sophisticated ad-hoc networks are also being developed which, in addition to enabling mobile nodes to communicate with each other as in a conventional ad-hoc network, further enable the mobile nodes to access a fixed network and thus communicate with other types of user terminals, such as those on the public switched telephone network (PSTN) and on other networks such as the Internet. Details of these types of ad-hoc networks are described in U.S. patent application Ser. No. 09/897,790 entitled “Ad Hoc Peer-to-Peer Mobile Radio Access System Interfaced to the PSTN and Cellular Networks”, filed on Jun. 29, 2001, in U.S. patent application Ser. No. 09/815,157 entitled “Time Division Protocol for an Ad-Hoc, Peer-to-Peer Radio Network Having Coordinating Channel Access to Shared Parallel Data Channels with Separate Reservation Channel,” filed on Mar. 22, 2001, now U.S. Pat. No. 6,807,165, and in U.S. patent application Ser. No. 09/815,164 entitled “Prioritized-Routing for an Ad-Hoc, Peer-to-Peer, Mobile Radio Access System”, filed on Mar. 22, 2001, now U.S. Pat. No. 6,873,839 the entire content of each of said patent applications being incorporated herein by reference.
As can be appreciated by one skilled in the art, when a node sends packetized data to a destination node, the node typically checks its routing table to determine whether the destination node is contained in its routing table. If the destination node is contained in the node's routing table, the data is transmitted via a path that leads to the destination node. If the destination node is not listed in the node's routing table, then the packet is sent to one or more other nodes listed in the node's routing table, and those other nodes determine if the destination table is listed in their routing tables. The process continues until the data packet eventually reaches the destination node.
As can further be appreciated by one skilled in the art, the “hidden node” problem is a classic problem for Medium Access Protocols (MACs) in these types of ad-hoc networks. The problem occurs when two radios (nodes) are transmitting outside the effective communication range of each other, but both are within the effective communication range of an intermediate node that is also participating in the network. If both of the two radios in the network attempt to communicate with the intermediate node at or near the same time, their signals can collide and/or cause packet corruption at the intermediate node which is the intended receiver. In this case, the two extremal nodes are “hidden” from each other.
The hidden node problem therefore reduces successful packet delivery at the intermediate node. Also, the more hidden nodes there are around the intermediate node, the more severe the packet corruption can be.
Accordingly, a need exists for a system and method for effectively and efficiently identifying nodes experiencing hidden node problems in a wireless ad-hoc communication network, so that routing through those nodes can be avoided if possible.